Circular
In order to produce a circular part on ordinary home shop equipment, it is necessary to mark a circle of the desired radius on the workpiece, perhaps cut it roughly to shape with a saw, and attempt to sand to the line on a disc sander while positioning the work by hand. It is essentially impossible to produce circular parts without flat spots and to produce duplicate parts.
Circular parts can be produced on tools where the work is rotated against a sanding block but equipment such as lathes and drill presses are not always available. Furthermore, it may be difficult to secure the work to the driving means and to control the finished dimension of the circular parts.